The one issue you may have getting wider 650 tires is that there are very few choices available. My Madone with 650 wheels will not fit a tire wider than a 25. I found only one 25 tires in the 650 size. The Felt may be the same. If it happens to accept a tire as wide as a 28, Terry sells a 28.

Here is a link to the 650 tire in a 25 width. Not too expensive so worth trying: http://www.amazon.com/Panaracer-Pase...racer+650+x+25